The electrocardiogram (abbreviated as either EKG or ECG) is a broadly used to obtain information ranging from a simple pulse (heart rate in beats per minute) to a very detailed description of heart activity. An EKG is obtained by recording changes in weak electrical potential coming from the heart to electrodes on the skin surface. Essentially, the EKG records an electrical side effect of heart activity. Depending on where the electrodes are placed, the changes in potential reflect depolarization and repolarization of the heart muscle along different axes. Changes in the potential along the major electrical axis of heart have a characteristic repeating pattern as shown in FIG. 1. The five visible spikes on the graph are called P, Q, R, S, and T waves. The most prominent feature of EKG graph is the tallest spike called R-wave. The top of the R-wave corresponds to the beginning of systole or ventricle contraction when blood is pumped into arteries. Heart rate is usually derived from the time difference between consecutive R-waves.
There is a need for an improved method for analyzing an electrocardiogram signal to reliably detect R-waves in order to yield a heart-rate value.
There is a particular need for an R-wave detection method that provides superior performance in applications where the electrocardiogram signal is used to monitor the heart rate of people engaged in physical activity. The R-wave detection method should accordingly be accurate in the presence of noise, including the presence of (1) motion artifacts from body muscle depolarization and repolarization; (2) changes in contact features between the electrodes and the skin; and (3) changes in overall amplitude and average level of the signal due to breathing or other phenomena that affect body conductance.
It is further desirable that the R-wave detection method exhibit a low detection latency so that it responds quickly to changing heart rates.
It is also desirable that the detection method be implemented with low cost components of small size.